Re: Changed oil, lost 3-4 mph on top end!@$?
 

What about the fuel?

Re: Changed oil, lost 3-4 mph on top end!@$?
 

Also check out if the boat was stored incorrectly over the winter. There are other threads on here about guys who have mysteriously lost 5 or more mph due to a hook developing from hanging the transom off the bunks. Just a thought...

Re: Changed oil, lost 3-4 mph on top end!@$?
 

Sounds strange. take some oil with you to the lake and retest, then change your oil back to the merc. Then retest right away. Only way to see if this is true.

Re: Changed oil, lost 3-4 mph on top end!@$?
 

Steve, I think you're on to something. The last time I ran the boat was 3 weeks ago and it was 45 air temp. It was 85, as you know, this last weekend.

BTW, thanks again for the help with the dock!

Re: Changed oil, lost 3-4 mph on top end!@$?
 

Mobil 1 15W50

Re: Changed oil, lost 3-4 mph on top end!@$?
 

That's your answer right there!! Cool air will give you the extra rpm's. :cool:

Re: Changed oil, lost 3-4 mph on top end!@$?
 

I have used the same valvoline straight 40-racing oil for the last 3 seasons in my 502's...never had a problem.

Re: Changed oil, lost 3-4 mph on top end!@$?
 

no big deal. you and Chris did all the work anyway.
besides , hanging out with you saved me hundreds of dollars in gas money. :drink:

Re: Changed oil, lost 3-4 mph on top end!@$?
 

I have seen this problem with a 4cyl nissan truck, the owner changed from 20w50 to 10w30 ,it made big differance.